Chrisd said:

"I will not be using any of my own existing soil in these beds since (A) I do not have enough soil to begin with and (B) my soil "sand/clay" sucks."

Welcome to the forum, you have come to the right place...

Your words sound like a whole lot of people who come here looking to start an organic garden, myself included. I too have/had soil that sucked; however with the help of others, an open mind, and a willingness to try things that, at the time didn't make sense to me, I have ended up with soil beyond my wildest dreams. With that in mind I offer the following:

The best soil to create a garden bed with is the soil you now have. It is much easier and cheaper to create a fertile soil from your existing soil than to correct some sucked up soil that was paid for. If your project were my project I would create lasagna beds over my existing soil. Lasagna beds are easy to create, require the materials you are already expecting to use in your compost pile, and best of all should be free of cost. IMO, looking into lasagna gardening will be time well spent and will allow you to still construct your compost piles (if you have the materials) at the same time.

As it relates to "rock dust", the link below will lead to much of what one needs to know concerning the use of rock dust in organic gardening. Please note the importance of organic microorganisms in the entire process; without organic microbes the journey is long and slow. This is why lasagna beds should work well in your plans. Other members may have suggestions to offer, some may not involve the use of "rock dust", but let that not hinder your intake of information is my suggestion; it will all fit together in the end is my experience. I trust this helps in some small way...

Blutranes

Here is a link that might be useful: A Rock Dust Primer

Blutranes - Thank you for the link. It was very informative. I am not interested in lasagna or sheet composting or using much of my own soil. I would like to make a complete compost with which to fill my raised beds. I do not mind spending a little money for certain ingredients. I figure I will need at least 10 cubic yards of compost to start with. I will be hot composting using piles. I have a tractor w/ loader so frequent turning isn't a problem.

ChrisD from FL, I am curious why you aren't interested in lasagna gardening. You expess a desire to make lots of compost to fill your raised beds. Lasagna gardens are basically the making of compost in position in a raised bed. You would just be skipping the step of putting the stuff in piles and letting it compost and then moving it to the raised bed. Why not just making the compost IN the raised bed? I do it all the time, works fabulously well, and the plants love it. You don't have to wait for the composting to work, and meanwhile you can have some compost piles on the side to add compost to the lasagna bed later when it settles. No reason that a sprinkling of this rock powder you desire couldn't be added to the lasagna bed.

Marcia

Chris, may I gently suggest that you may not know enough about soil to know what you want or need? And I will assume that the 'fl' after your name indicates Florida. I googled Florida soils, and none of them indicated the presence of clay, just sand of different kinds, and some sandy loam. If you had a combination of sand and clay, that would be a good thing. Dark sand is not clay. The human diet needs silica, and the best place to find it is in soil. And without it, you can't grow decent watermelons.

Planting in what is virtually straight compost is far from ideal. There is more to soil (or even a growing medium) than just nitrogen, potassium, phosphorus and some minerals. A growing bed with high percentages of compost and manure tends to produce a bed that is too high in phosphorus and potassium, which can cause several types of vegetables to taste bitter. High phosphorus ties up zinc, so even if it's in your soil, it's not available to the plants.

Blutranes gave you good advice. It's easier to amend existing soil than it is to create it from scratch. Your soil, whatever it is, has something beneficial to offer your plants. Have you had a soil test done? I would suggest doing so, and asking for info on trace minerals also. You might need a particular type of rock powder, from another area. If you use local powders, it will likely be of the same mineral makeup as your soil. If your soil is lacking something vital, the local rock powders probably will be, too.

What is your calcium level? Most sandy soil is low in calcium in areas of high rainfall. Only one kind of manure generally contains calcium. Do you know which? Magnesium? Also a problem in sandy, rainy areas.

Nitrogen? You only need about 5% If you add too much nitrogen, when it leaches out with rain or irrigation, it will take calcium out with it, and magnesium levels will rise.

Do you need sulfur? If you're low, it will affect yield and keeping quality of your produce.

Some soils are high in sodium, some are low. It's nice to know which you have. A deficiency can affect certain crops, but you may be adding enough with the manure you're adding. But too much manure can increase the sodium levels to where you're going to have trouble.

Boron is low in many areas of the U.S., from coast to coast. Adding it without knowing how much you need is foolhardy. If you add too much, your seedlings will be harmed. If you don't add enough, your plants still suffer.

Most soils seem to be low in Copper. If you have a kind of peat/muck soil, it's practically guaranteed.

Where are you in regards to the other vital trace minerals, Molybdenum, Manganese, Zinc? Without a soil test, you just can't know.

Blutranes suggested building beds on top of your soil. This would be useful in at least two ways: earthworms and other soil fauna will bring native soil up into your beds, and the roots of your plants can go down into the soil to find more moisture and nutrients that they need. He wasn't necessarily suggesting that you MIX your soil and compost, just let them work together.

Sue

If you want to create raised beds and not use your existing soil; I would buy topsoil, not rock dust, and mix it with compost.

IMO, The rock dust plus compost mixture would still be missing some parts of the soil structure.

Soil is silt, sand, clay, organic matter, water and air. I think rock dust might be the silt and sand parts, but missing the clay parts?

Topsoil is usually easy to find... and its easy to improve by adding compost. Compost is the organic matter portion of the soil.

And generally, depending upon the topsoil, you could mix two parts topsoil to one part compost and probably have a good start. If the topsoil was low on organic matter, then you alter the mix to increase the portion of compost. I would continue to topdress the raised beds with compost annually after its installed.

On the other hand, the "topsoil", at best, would probably be just what he already has and doesn't want to use, except that he'd have to pay for it to boot, and at worst would be a big lump of subsoil and old refrigerators (if unscreened).

However, at least the raised beds would stay raised, unlike if he filled the raised bed with just compost. Compost decomposes -- that's what it's supposed to do.

Poor Chris must be frustrated by now.

Yeah, I got the impression OP wanted raised beds... and if that is case, he is going to have ADD material. Lasagna alone is not going to be enough to make a raised bed.

"I think rock dust might be the silt and sand parts, but missing the clay parts?"

Not exactly; glaciers retreating during the last ice age created rock dust as the ice ground against rocks/boulders, thus it really is soil. This is one of the reasons soils in the north are endowed with more minerals than soils in the south where the glaciers didnt cover due to climate. Rock dust today is a waste product of the gravel and cement industry. Those rock particles that are too small for use are considered garbage that has to be disposed of. The industry tries to sell the rock dust of $1.00 per ton; but the problem is cost of shipping and handling, so they have to pay to get rid of it. No one has any use for the rock dust that has the consistency of flour except gardeners and farmers. Rock dusts are pure minerals found within the soil. The link provided explains it a lot better than I just did.

Chrisd said:

"I am not interested in lasagna or sheet composting or using much of my own soil."

Although one may not feel their soil is worthy, Mother Nature will have her say in the matter. As an example, eight weeks after a corn seed is planted its main root has grown 4 feet into the soil. The feeder roots have spread 5 feet in all directions at a depth of one foot below the soil surface. The mass of roots found on vegetable crops actually mine the soil for minerals and water. Thus, in order to keep roots out of native soil one would have to create a vegetable bed at least 5 feet deep and who knows how wide to insure said roots donÂt get into the native soil. The link below leads to a page that explains the root system of most of the vegetable crops we tend to grow (thanks Gonefishin). There is a lot of reading, however the page does provide pictures of root systems so one can get an idea of just how extensive the root systems in our gardens really are. As I said, Mother Nature will have her way in the matter, weather we like it or not.

Chrisd, your plan will work of course; we are just trying to save you a little work. Following the lead of Belgianpup, another benefit of creating a lasagna bed is the fact that the bed will kill most weeds within the bed as it decomposes. Having little or no weeds to pull during the season is a plus I am truly grateful for. I trust we have been of some small serviceÂ

Blutranes

led zep - Sheet composting just doesn't appeal to me. Too passive I guess. I like the big piles of steaming organic material and the relatively fast rate of decomposition.

belgianpup - I will agree that I do not know enough about soil; hence my presence here asking questions. I do not wish to plant directly into compost per-se but more-so into an amalgamation of appropriate ingredients of which compost is a constituent. Maybe I should have used different wording to describe my desired final product. Lets replace the term "compost" in my initial inquiry with "balanced, amended soil". Maybe that would placate yall's desire to nitpick.

Despite the fact that my existing soil may well be worthy of horticultural use, I would not like to use it. I have already had to have ten cu. yards of topsoil delivered, just to level the terrain on which my raised-beds will be situated. Though I could use this material as the soil-base for my beds, it did not meet my standards due to its debris content (glass, plastic, rusty nails) and lack of source info. I am not stating that soil will not be used, just that I will not be using any of that which I already have. I plan to find a source of clean, rich topsoil even if I have to dig it myself.

Your assumption that I would be using a compost that is too high in manures is incorrect. The manures listed are those that I currently have available for use. I will not be haphazardly introducing them without forethought of there affect on the final product.

Thanks for your response. You have highlighted some interesting food for thought to study whilst engineering my soil. I really do appreciate it.

joepye - Thanks for the input. I guess I'll make my first initiative finding a high-quality topsoil.

Chris

Hi Chris,

I have 8 raised beds, used the lasagna method for them all. Also have 3 large compost piles. Never thought of one being passive and the other active. Sounds like you can get good ingredients for a lasagna bed, and the only problem that you have is it doesn't sound hard enough for you?!? You pile up the layers, throw a little topsoil or something directly around what you are planting, and you are ready to go.

You don't need to wait the month(s) for your compost pile to work, you can plant immediately into a lasagna bed if you put some type of soil or finished compost around your plants or under your seeds. Another advantage to this method is that you don't have to buy stuff (except maybe a smidge of topsoil) to fill all those raised beds. You don't need to work your own soil into it at all, although worms and roots will do that over time. Seriously, what is the reason for wanting to use a more difficult and expensive method?!? It doesn't make sense.

Marcia